Although this method is already completely satisfactory, the present invention disclosure will further perfect it, so as to improve its precision and, where appropriate, to use it for imaging in three dimensions.
For this purpose, a method of the kind in question is characterized in that it includes a correction step during which the movement parameter is processed so as to remove the effects due to the compression component of said mechanical wave.
Thus, even when a pulsed thrust is used, if the compression component of the elastic mechanical wave that results therefrom disturbs the measurement of the movement parameter, only the effects of the shear component are taken into account. When instead of a pulsed mechanical wave a sustained wave is used, for example in order to carry out a relatively long measurement, such as for three-dimensional imaging, the compression component of the mechanical wave is still present during the time of measuring the movement parameter and it therefore greatly disturbs this measurement. The processing according to the invention makes it possible to eliminate this disturbance and, where appropriate, to map the viscoelastic parameters of the medium in two or three dimensions.